Logging while drilling system



June 24, 1969 A p, Rmx-WERl JR" El AL 3,451,263

LOGGING WHILE DRILLING SYSTEM Sheelfl Filed Nov. 29, 1967 June 24, 1969 Filed Nov. 29, 1967 A. P. RICHTER,4 JRu ETAL LOGGING WHILE DRILLING SYSTEM Sheet 'MlJw-THC'LC.

United States Patent O 3,451,263 LOGGIN G WHILE DRILLING SYSTEM Albert P. Richter, Jr., and James D. Bruner, Houston,

Tex., assignors to Texaco Inc., New York, N.Y., a

corporation of Delaware Filed Nov. Z9, 1967, Ser. No. 686,566

Int. Cl. E211) 29/00 I U.S. 'CL 73-152 3 `Claims ABSTRACT OF THE DISCLOSURE Apparatus for continuously measuring the surge pressure developed when a drill string having a drill bit at the end thereof is run into an earth borehole lled with drilling mud. Incorporated in the drill bit per se isA ra pressure sensing element which actuates a'f't'ly located pressure transducer. Electrical signals representative of the surge pressure are transmitted from the pressure transducer to a transducer signal pocessing circuitry unit and then to a recording unit, said units being incorporated in the drill string above the drill bit.

Background of the invention This invention pertains in general to a method and apparatus for detecting, measuring and recording the surge pressure below a drill bit at the end of a drill string as the drill string is run downwardly into an earth borehole filled with drilling mud or uid.

One important parameter in connection with the making of a borehole in the earth for the purpose of seeking subsurface oil, gas or minerals is the magnitude of the surge pressure below the drill bit. While the borehole is being made in the earth by a rotating drill bit, the borehole has drilling mud circulating therein. However, from time to time, for various reasons, the rotation of the drill bit is stopped and the circulation of the drilling mud is also stopped in order to raise the drill string, having the drill bit at the end thereof, out of the borehole. For example, it may be that the drill bit has to be changed. Upon lowering the drill string back into the mud filled borehole it often happens that the drill string is dropped rapidly through an appreciable distance and there occurs immediately below the drill bit a rather high surge pressure. This surge pressure is comprised of among others three components; one, the pressure produced by the bit acting as a piston in the borehole; two, the pressure required to get the mud displaced by the drill string into motion; and, three, the pressure necessary to overcome the viscous drag of the mud column. If these components of pressure are high enough, damage to the surrounding formations would result and would possibly fracture the formation with the consequent loss of circulation of the drilling mud. In some cases the pressure that will fracture a formation is very near the pressure produced by the mud weight necessary to prevent a blowout. In such cases, the surge pressure is a critical item indeed. Hence, it is desirable to measure the magnitude of the surge pressure.

Summary of the invention One object of the invention is to provide a method and apparatus for determining the surge pressure below a drill bit.

Another object of the invention is to prevent formation fracturing and loss of circulation of the drilling mud while running the drill string into a mud filled borehole in the earth.

In accordance with an illustrative embodiment and practice of the invention there is incorporated in a drill bit at the end of a drill string a pressure sensor for meas- 3,451,263 Patented June 24, 1969 p ICC uring surge pressure of drilling mud in an earth borehole as the drill string is being run down into the mud iilled borehole. The sensor actuates a remotely located transducer. Electrical signals representative of the surge pressure beneath the bit are transmitted to a transducer signal processing circuitry unit and then to a recording unit, said units being incorporated in the drill string above the drill bit.

Other objects and advantages as well as the various features of novelty which characterize the invention are pointed out with particularity in the claims annexed herewith and forming part of the specification. For a clearer understanding of the invention, its operating advantages and the specific objects attained by its use, reference is to be had to the accompanying drawing gures and descriptive matter in which there is illustrated and described an illustrative embodiment and practice of the invention.

Brief description of the drawings FIG. 1 is an elevation View showing a rotary drilling apparatus as it is being lowered back into an earth borehole filled with drilling mud; said apparatus including the surge pressure measuring apparatus in accordance with the present invention.

FIGS. 2a, 2b and 2c are cross-sectional elevation views of different sections of the lower end of the drilling apparatus of FIG. l and including the rotary drill bit of the apparatus; FIG. 2a showing the uppermost section, FIG. 2b the next lower section, and FIG. 2c the lowermost section below that of FIG. 2b.

Detailed description of the invention In the drawing figures like elements or components are designated by the same reference numbers throughout.

In FIG. l there is illustrated a drill string designated generally by the reference number 10, which drill string is made up of, among other things, a series of drill pipes coupled end-to-end. Located at the lowermost end of drill string 10 is a conventional rotary drill bit designated, generally, by the reference number 12. As suggested in FIG. 1, drill bit 12 at the end of the drill string is being lowered into an earth borehole 14 which traverses various earth formations and the borehole 14 is lled with drilling mud or -drilling fluid. The drilling mud being designated generally by the reference number 14a. As shown in FIG. 1 the drill bit and drill string, although well down in the mud lled borehole, have not as yet reached the bottom thereof.

Referring now to FIG. 2a there shown is a capsule designated generally by the reference number 16. As indicated `by the label, capsule 16 houses a recording unit and associated circuitry. Capsule 16 is a sealed container adapted to withstand pressures of about 14,000 lbs. per square inch, or more as required. As shown recorder capsule 16 is mounted coaxially within a special sub 18 which is a conventional drill collar that has been hollowed out for the purpose of receiving capsule 16. Capsule 16 is supported within special sub 18 by means of a plurality of longitudinal members 20 or runners which are welded to the outside surface of capsule 116 along substantially the entire length thereof and to the special sub 18. Capsule 16 is closed at its upper and lower ends by two end caps 22 and 24, respectively, or -bull plugs as they are often called. Details of the construction of capsule 16 are disclosed in more detail in U.S. patent application Ser. No. 674,335 entitled Logging While Drilling System filed Oct. 10, 1967 in behalf of Albert P. Richter, Jr. and James D. Bruner. As indicated in FIG. 2a, end cap 24 has a threaded aperture therethrough which receives a threaded conduit 26. The conduit 26 has an annular groove formed on the outside surface thereof and this groove contains a. sealing Oring 28.

Coupled to the lower end of the special sub 18 by means of conventional API tool thread is another special sub 30. Mounted coaxially within special sub 30 is another sealed capsule 32 similar to capsule 16. Capsule 32 as indicated by the labeling contains transducer signal processing circuitry. Capsule 32 is mounted on welded runners 34 to the special sub 30 in the same manner as capsule 16 is mounted by means of the runners 20 to the special sub 18. Capsule 32 is provided with two end caps 36 and 38 or bull plugs, the end caps 36 and 38 being at the upper and lower ends of capsule 32. More details on the construction and arrangement of capsule 32 is disclosed in the aforementioned U.S. patent application Ser. No. 674,335.

End cap 36 as shown in FIG. 2b has an aperture therethrough which receives the conduit 26. Conduit 26 carries therewithin electrical conductors 42, which conductors transmit signals from the transducer signal processing circuitry -within capsule 32 to the capsule 16 which contains a recording unit such as a magnetic tape recorder and associated circuitry. As shown in FIG. 2b end cap 38 has a threaded aperture therethrough which receives the end of a threaded oil-filled conduit 44. At the point where conduit 44 enters the aperture in end cap 38 a pair of annular grooves is provided in the outside surface of the conduit and these grooves receive the sealing O-rings 46.

Coupled by means of conventional API tool threads at the end of special sub 30 is another special sub 48. Coupled to the lowermost end, as shown in FIG. 2c, of specal sub 48 is the drill bit 12. As shown in FIGS. 2b and 2c conduit 44 extends coaxially within special sub 48 from end cap 46 through special sub 48 to the drill bit 12. Drill bit 12 'has a central opening formed therein for receiving conduit 44. An annular space is formed in the drill bit for receiving an `O-ring seal 50. .At the lowermost end of conduit 44 there is mounted a pressure sensing element, or sensor, 52. Pressure sensor 52 may, for example, be a diaphragm or piston type of pressure transmitting element. Conduit 44 is lled with oil column 54. The oil column 54 lls the entire hollow in ner passage of conduit 44 from the element 52 in the drill bit at one end to a pressure transducer 56 located at the other end mounted in the end cap 38. Coupled to the pressure transducer 56 in end cap 38 are the electrical conductors 58 which transmit electrical signals from transducer 56 to the transducer signal processing circuitry. Signals from the transduoer signal processing circuitry in capsule 32 are then transmitted via the conductors 42 through conduit 26 to the capsule 16 to the recording unit and associated circuitry. With the apparatus, shown more particularly at FIG. 2c, the determination of surge pressure of the drilling mud below the bit as the drill string and bit 12 are being lowered into borehole 14 may be determined by the following method:

As the drill string and bit are lowered into the borehole and traverses various earth formations thereof, the pressure sensing element 52 is actuated by the surge pressure of the drilling mud. The element 52 transmits this force to the oil lled column 54 which, in turn, transmits 4- this force to the transducer 56. Transducer 56 may, for example, include a strain gauge conguration. The signals from the transducer 56, which are representative of the surge pressure transmitted through the oil filled column 54, are thence transmitted via the conductors 58 to capsule 32 and thence in the manner hereinbefore explained to the capsule 16 whereat they are recorded. Thus as the drill string and bit are passed downwardly through the mud lilled borehole there is obtained simultaneously a record of the surge pressure below the drill bit correlated with the velocity and depth of the drill bit in the borehole. The velocity being recorded by means of the rec-order 60. Recorder `60 shown in FIG. 1 is a velocity measuring device for the purpose of measuring how fast drill string 10 is advancing downwardly into borehole 14.

While a specific embodiment and practice of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it is to be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. Apparatus for logging at least one parameter determined in a earth borehole containing drilling mud comprisingz' a drill string having a drill bit at an end thereof;

means in said drill bit for detecting at least one parameter in the borehole;

means in said drill string for recording the detected parameter;

said detecting means in said drill bit detecting surge pressures below the bit as the drill string and bit are passed into the mud containing earth borehole.

2. Apparatus for logging surge pressure below a drill bit at the end of a drill string as the string yand bit are passed into an earth borehole containing drilling mud comprising: a pressure sensing device incorporated in the drill bit and located in the bit so as to sense the surge pressure of the drilling mud as the bit passes through the drilling mud in the borehole; housing means mounted in the drill string and including therein a transducer for converting pressure energy to electrical signals, circuitry for processing the electrical signals and a recording unit for recording the signals; and, means for transmitting pressure sensed by said device to the transducer.

3. Apparatus according to claim 2 wherein the pressure sensing device includes a piston, and wherein the lastmentioned means is a lluid-lled conduit extending from the piston to the transducer.

References Cited UNITED STATES PATENTS 2,925,251 2/1960 Arps 175-39 3,203,243 8/1965 Lyles 73-l52 X 3,374,341 3/1968 Klotz 175-48 X RICHARD C. QUEISSER, Primary Examiner. JERRY W. MYRACLE, Assistant Examiner. 

